A Holistic Approach to Inflow and Infiltration

Columbus goes against the grain and includes residential lateral lining to reduce I&I and fulfill consent decrees

A Holistic Approach to Inflow and Infiltration

Matt Wagner, Bryant Bailey and Dan Bokrors (from left) of BLD Services prepare to line a junction of a residential sewer lateral for the Columbus Department of Public Utilities, part of a program to address inflow and infiltration from private properties. 

Photography by James DeCamp

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The story’s familiar: The EPA issues consent decrees to a municipality for sanitary and combined sewer overflows, forcing rehabilitation of existing underground infrastructure to protect the public and environment from raw sewage spills. The city of Columbus, Ohio, is no exception. 

In a concerted effort among many midwestern state EPAs to reduce increasing water pollution and residential backup complaints, Ohio EPA issued Columbus two consent decrees were in 2002 and 2004, for SSOs and CSOs, respectively. This became a catalyst for the city to develop a wet weather management plan in 2005. 

This plan included plant upgrades, construction of relief pipes/tunnels, pipe upsizing, mainline pipe and manhole rehabilitation, all of which reduced inflow and infiltration into the system. The city also added aggressive preventive cleaning and root removal to its existing CMOM program to reduce basement water backups. 

Going with the flow

The Public Utilities’ Sewerage & Drainage Division, which is responsible for sanitary sewers and stormwater management, knew their first task was measurement. They needed hard data to confirm their biggest problem areas, and the actual extent of the issue. They decided to launch some combined flow monitoring and sewer modeling pilot areas.

The division has its own in-house flow monitoring crew, and permanent flowmeters installed throughout the system allow continuous recording of operation. Crews also install temporary flowmeters in areas where they want to identify specific hydraulics for more tailored solutions.

Groundbreaking decision

City Council came up with an integrative, holistic approach to rehabilitation efforts. 

Instead of simply treating overflow symptoms with massive, time-consuming underground construction of tunnels that would cost billions, they asked the more direct question: Why not invest that money in eliminating the actual source of I&I? Everyone knew from location patterns of their worst overflows and basement backups that a significant percentage of that I&I was coming from private residential laterals. 

Repairing those laterals from the foundations to the main was the most simple, direct strategy. But first, city leaders had to be convinced that it was a good idea to spend public money repairing private property. Then there was the logistical challenge of the sheer scope of work they were certain would be needed. Finally came the highest hurdle of all: getting citizens on board, because the strategy couldn’t succeed without their support.

It was a legally tricky jurisdiction issue, but not impossible. Council members were determined. Blueprint Columbus was established in 2012 and continues successfully today, solving a critical issue facing nearly every American city. 

Old pipes

With a current population of just over 915,000, Columbus is the 14th largest city in the country. The public utilities department serves 906,000 customer accounts — city residents and businesses, as well as contracts with surrounding suburbs — and its S&DD is responsible for both. 

Sewer and water infrastructure dates back, in some parts, to the 1880s. The majority, however, was put in the ground post-Great Depression through the 1960s, when the city — like many in the Midwest — experienced its greatest growth. This puts the average age of the collections system at about 75 years, with some a bit younger and much of it significantly older.

Central Ohio is relatively flat, but Columbus’s 4,500-plus-mile collections system was designed to take advantage of gravity flow as much as possible. The system feeds into two wastewater treatment plants. The Jackson Pike plant is designed for 68 mgd and can handle 150 mgd peaks, while the Southerly facility was designed for 114 mgd with 330 mgd peaks.

Confirming data

Columbus’s combined collections system had its mainline and manhole I&I issues, but all decision makers involved were sure that if they could effectively stop what was flowing in from the laterals, they could meet the demands of the consent decrees. 

As part of the original 2005 WWMP, the city’s Clintonville and Linden areas had gotten their mainline sewers lined previously, in response to the original consent order. That meant any I&I still coming in had to be from the laterals, so a pilot flow metering project was set up there. This was done with a limited number of residential laterals lined on a voluntary basis, until City Council could come up with a way to broaden their legal access to private lines. 

This would show a contrast between sewers that had been lined only on the mains, with others that also had the laterals lined. They could be in streets right next to each other, for direct comparison. Crews also installed sump pumps in houses in a different area, and monitoring meters measured how this affected groundwater around the foundations. They added flowmeters in sewers immediately downstream to gauge what effect the sump pumps had on reducing sanitary sewer flows, since they knew much of the water enters through the 4- to 6-inch transition from house to lateral just outside the foundation wall. 

A concerted effort was made to distribute lateral lining or sump pump pilots among different types of properties, representative of those in all citywide areas that would need to be addressed. 

New ground

With mains taken care of and lateral pilot programs in place, the Sewerage & Drainage Division turned its attention in 2006 to CMOM initiatives that focused on structural integrity and maintenance, creating a Large-Diameter Sewer Assessment program. 

“Because many of our internal crews don’t possess the equipment to televise sewers larger than 42 inches, we needed this program,” recalls Nick Domenick, P.E., project manager for the city of Columbus, Department of Public Utilities.

“Since our large-diameter sewers had never been fully assessed previously, we thought it’d be a good chance to get an idea of their condition. Given the expense of televising that sheer number of sewers, we developed a program to prioritize them.”

The idea was to televise about 40,000 lineal feet of large-diameter sewer every year for 20 years. “We just have that much LD footage,” explains Domenick, “so we started doing that, and realized that by releasing larger packages of work, we were able to achieve some economy of scale.”

The division started putting together 80,000- and 100,000-foot-long work packages, and recently completed everything within the sanitary system. They’re now shifting focus to televising their stormwater system. “Through the use of consultants and CCTV vendors televising every lineal foot of large-diameter sanitary and combined sewer we have, we’re making strides on our storm side, too,” Domenick says. The result is identification of a significant quantity of necessary work, about $200 million worth, which needs to be done within the next 5 to 10 years.

“The challenge now is prioritizing that work from an affordability standpoint, making sure we don’t have a huge hit to our ratepayers, that we’re maximizing existing service life, and performing intervention at the right time. Because when you assess these sewers and you see exposed rebar on hundreds of thousands of feet of pipe, it’s like, ‘Gosh, where do we start? Which one takes priority?’ This is where classic criticality analysis, looking at likelihood and consequence of failure, comes in. That affects the timing in our overall program, what part of town it’s in, and packaging the work into logical groupings,” Domenick says.

Bold approach

Soon, data from the pilot programs began coming in, confirming suspicions about the bulk of their I&I. Meanwhile, City Council had been working on the legal nitty-gritty of getting legal access to residential laterals.

“We needed something to give us the authority to spend money on assets located on private property, which we don’t own,” Domenick recalls. In a bold move, the City Council enacted an ordinance declaring I&I an official public nuisance. This gave them authority to do what was necessary to stop the nuisance at its points of origin. 

This would be accomplished by asserting a temporary Right of Access to perform work on the laterals. Because CIPP or sliplining would be used, ordinance language allowed trenchless access to the pipe at the main, or through a clean-out; and within reason, the work could go on as long as it took to complete. Ownership of the assets would never actually change hands. 

One point used to justify the expense of lining residential laterals was the alternative: having to build large-diameter tunnels to capture overflows, while still not addressing the problem’s root cause. 

“Let’s actually go in and try to get the water out of the system,” was the idea, according to Domenick. “It might not eliminate the tunnels entirely, but it might shorten them, or make them a smaller diameter,” and therefore less costly. 

Consumer education

That decision made, the next step would be most crucial: Selling it to Columbus citizens. 

“The biggest challenge is the public interaction component of it,” Domenick states unequivocally. “Educating your customers about the value of it, and why this is the best expenditure of the ratepayer’s money. I think you don’t experience the ‘NIMBYism’ if you do an adequate job of explaining to them the rationale of why you want to do this in their neighborhood.” 

The job of explaining this new, far-reaching, long-term program to the public fell largely to Blueprint outreach personnel, which included the help of local public relations firms. 

The leaders used all communication channels at their disposal including major social media, and built an extensive page on the city’s official website dedicated to introducing, explaining and tracking Blueprint Columbus’s progress. Particularly effective was a promotional video they produced and posted there.

The city also leveraged traditional publicity methods with an ongoing program of news releases to media outlets. They held numerous outreach and educational sessions for a community advisory panel that had been integral to helping develop the WWMP update, and for City Council members, regarding the challenges posed by I&I, so they could be informed sources for public inquiry. Public meetings were held, along with presentations at area commission meetings.

Ultimately, these efforts were a great success, according to Domenick, addressing the citizens’ response. “They’re smart. They get it. I think they actually realize the value of receiving a newly rehabilitated lateral. It means they don’t have to pay for root removal on it. A lot of these people are grateful it’s being done because it’s a real benefit to them.”

Getting to work

As the publicity machine was revving up, the actual work was being initiated. The largest part of the lateral lining went to BLD Services of Kenner, Louisiana. Their process works from the main line and doesn’t require clean-out access. 

In the initial project areas, Sewerage & Drainage Division televised the laterals prior to releasing the bid package, so they had a better idea of whether or not they required significant point repairs or root removal prior to lining. 

Domenick says they performed a sort of regression analysis. “We did some statistics on the number of laterals that actually needed a point repair. After we released the bid packages and started doing the work, we began keeping statistics on the ones that had a ton of roots in them, those that may have needed a cleaning to remove them. There are technologies out there now that allow for root removal from the main, another advancement I think has really yielded a lot of benefit to both us and the contractors. We don’t have to go onto private property to install that clean-out, and incur that cost. And from a customer service standpoint, we don’t have to tear up their yard. It also eliminates the need for potentially having to dig the lateral up for roots, too.” 

They started out with 500 laterals per contract, then realized the contractors could handle more and still get done within needed timelines. On average at this point, they’ll release 750, and in some cases up to a thousand. Individual project areas are usually somewhere between 500 and 750. “We do have one coming up that’s going to be 1,200, and there’s not going to be any stop to this in the near future. It’s going to be multiple contracts for the next 20 years.”

BLD was awarded the projects more by virtue of their size, which allows them to achieve economies of scale in material sourcing. 

“They’ve won most of the projects to this point,” Domenick says. “I think we’re on our eighth or ninth lateral lining project at this point. We’re about 4,000 or 5,000 laterals in, of the Blueprint areas we’ve gone into. And we’re only in our second of 20 Blueprint areas.” 

Post-construction sewer flow monitoring has confirmed that the combination of mainline sewer, manhole and lateral lining has been reduced overall I&I by an average of 57%.

“We’ve largely completed all our improvements to satisfy the CSO consent decree,” Domenick says. “It’s the SSO one where the bulk of the work remains.”


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